DUAL Table in Oracle

DUAL Details : http://en.wikipedia.org/wiki/DUAL_table

SELECT 1+1
FROM DUAL;
 
SELECT SYSDATE 
FROM   DUAL;
 
SELECT USER 
FROM   DUAL;

INSERT ALL 
INTO customers VALUES (2, 'John Lincoln', '200 Oracle Plaza', 'Sunnyvale', 'CA')
INTO customers VALUES (3, 'Peter Doe', '300 Oracle Plaza', 'Sunnyvale', 'CA')
select * from dual;